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An exhaust flange is a device used to attach an exhaust pipe to an exhaust manifold or another piece of exhaust pipe. Commonly designed to sandwich an exhaust gasket between the exhaust manifold and the exhaust pipe, the exhaust flange is manufactured to an exact angle to eliminate the chance of any exhaust leaks when tightened. Modern exhaust systems use a ball-type socket that eliminates the need for a gasket as the exhaust flange tightens against a preformed exhaust pipe to create a leak-proof seal.
Nearly every type of exhaust, from manifolds to tubular headers, incorporates the exhaust flange in some form to prevent exhaust leaks. Some versions of the flange utilize what is known as a donut gasket to assist in sealing the system. The donut gasket is a round gasket that uses a flat and smooth center hole to ride solidly on the exhaust pipe. The outside diameter of the donut gasket is manufactured with a slight angle on each side that is sandwiched into the flange on the exhaust manifold and the exhaust pipe. As the exhaust flange is tightened, the donut gasket is drawn into the flange and creates a solid seal that contains the exhaust sound, fumes and heat.
The typical exhaust flange is nothing more than a stamped steel collar that is held in place on the exhaust pipe by a slight flare on the exhaust pipe. There are usually two or three flange bolts used to secure the flange when tightened. Some flange bolts use a heavy coil spring to maintain some pressure against the flange even when the bolt might become loosened. This coil spring is placed over and around the flange bolt before it is threaded into the flange nut. Once tightened, the spring is compressed against the flange plate and exerts pressure against the flange.
Due, in part, to the high heat encountered by the flange bolts positioned in close proximity to the exhaust pipe and the harsh environment underneath the vehicle on a daily basis, the exhaust flange bolts are usually extremely difficult to save when making repairs or upgrades to the exhaust system. The bolts are typically cut off with a torch and then removed from the exhaust manifolds with locking pliers. New flange bolts are installed into the manifold using a coating of anti-seize compound to make removal less difficult at the next maintenance date or repair interval.